Numerical Simulation of Summertime OH Concentrations in China Since the Implementation of the Air Pollution Prevention and Control Action Plan

The OH radical is the primary tropospheric oxidant, accounting for the oxidation capacity of the atmosphere. The GEOS-Chem model was used to examine the impact of anthropogenic emission and meteorological parameter changes on summertime OH concentrations in China since the implementation of the Air Pollution Prevention and Control Action Plan. Our modeling results for the years 2014–2017 demonstrate that the summertime OH concentrations in China exhibited an overall upward trend with the fastest increase occurring around 30°N over eastern China; the North China Plain was also simulated to have an obvious upward OH concentration trend of 0.1 × 10⁶ molecules cm⁻³ a⁻¹ while the Pearl River Delta experienced a weak downward trend. Further sensitivity experiment simulations showed that changes in both meteorology and anthropogenic emissions over the years 2014–2017 contributed to the increases in OH concentrations in the North China Plain, wherein the contribution of anthropogenic emissions was significantly larger than that of meteorology (10% vs. 1.5%). Meteorology played a major role in OH concentration increase around 30°N over eastern China. Further meteorological analysis demonstrated that the meteorological variable with the greatest contribution was solar shortwave radiation, which can explain the changes in the OH concentrations over a large fraction of China during 2014–2017. However, the role of solar shortwave radiation was offset by the boundary layer height in impacting the changes in OH concentrations during 2014–2017 in the North China Plain.